The embodiments described herein relate generally to superconducting coil systems, and more particularly, to methods and systems for protecting superconducting coil systems from damage due to quenching.
Some electrical machines, such as generators or motors, can have a rotating rotor and a stationary stator. The current density and thus the specific power of these machines can be increased, and the efficiency of the machine can also be increased by the use of cryocoolers, wherein superconducting coils of electrical cryocoolers have to be kept at a required low temperature by a coolant. The use of superconducting coils in some electrical machines can result in an increase in electromagnetic forces generated by the coils and an increase in flux densities within the machines.
Superconducting coils typically have near zero electrical resistance. However, superconducting coils may undergo a transition from a superconducting state to a normal, conductive state due to an abrupt change in the magnetic field or a temperature anomaly. This transition of the superconductive state is known as quenching. More particularly, quenching is an abnormal termination of magnet operation that can occur when a superconducting coil enters a normal (resistive) state. Sometimes quench can occur when the magnetic field within the magnet is too large and/or the rate of change of the magnetic field is too large which can result in eddy currents and increased heating to raise the temperature of the coils and surrounding regions. The increased temperature of one coil may increase the temperature of adjacent coils leading to a chain heating reaction. An explosion may occur as the energy in the magnetic field is converted to heat and a rapid boil-off of any cryogenic coolant occurs. Sometimes, when a large magnet undergoes a quench, an inert vapor can be formed by the evaporating cryogenic fluid which can present an asphyxiation hazard to operators by displacing breathable air. Moreover, an abrupt decrease of current can result in inductive voltage spikes and arcing which can damage cryocooler components by localized heating, high voltages and/or large mechanical forces.